This invention relates to an improved combustion process for internal combustion engines as well as to an arrangement for accomplishing the combustion process.
In a known internal combustion engine, a mixture of gaseous fuel and air is fed into a cylinder through an air inlet duct during a suction stroke of a piston in the cylinder, the mixture is compressed during a compression stroke and is ignited either by means of a spark or by self-ignition due to the increase in temperature caused by the compression. In order to facilitate ignition of such a gaseous fuel/air mixture when using spark ignition, the ignition plug may be located in a separate auxiliary chamber or similar space in communication with the combustion chamber of the cylinder and into which a small amount of additional gaseous fuel is fed for enriching the fuel/air mixture. It is also known to feed additional fuel into the cylinder when using compression ignition so as to enrich the mixture before ignition and thereby ensure proper ignition. In accordance with these concepts, however, the mixture in the cylinder is lean, whereby the combustion process in question is a so-called lean burn process. A lean burn combustion process is one in which the fuel and oxygen are present in proportions such that theoretically all the fuel can be burnt.
A disadvantage of the combustion processes that are carried out in the known engines referred to above is that the mean effective pressure that is generated in the cylinder is only about 12-14 bar. Moreover, in the known engines it is not possible to achieve scavenging of the cylinder by providing for the inlet and outlet valves to be open simultaneously, because some of the gaseous fuel fed through the inlet duct would pass directly into the outlet duct. An advantage of the lean burn process, on the other hand, is that the exhaust gases include a lower concentration of nitrogen oxides, NO.sub.x, than the exhaust gases produced by rich burn processes, in where there is excess fuel that cannot be burned. Further, in a lean burn process the risk of untimely self-ignition is reduced or avoided.